Using gait parameters to detect fatigue and responses to ice slurry during prolonged load carriage

• Prolonged load carriage leads to unstable gait characteristics in the frontal plane.
• Gait instability can be a non-invasive proxy for detecting exertional heat stress.
• Ice slurry ingestion can alleviate some undesirable changes in gait patterns.

This study examined (1) if changes in gait characteristics could indicate the exertional heat stress experienced during prolonged load carriage, and (2) if gait characteristics were responsive to a heat mitigation strategy. In an environmental chamber replicating tropical climatic conditions (ambient temperature 32°C, 70% relative humidity), 16 males aged 21.8 (1.2) years performed two trials of a work-rest cycle protocol consisting two bouts of 4-km treadmill walks with 30-kg load at 5.3 km/h separated by a 15-min rest period. Ice slurry (ICE) or room temperature water (29°C) as a control (CON) was provided in 200-ml aliquots. The fluids were given 10 min before the start, at the 15th and 30th min of each work cycle, and during each rest period. Spatio-temporal gait characteristics were obtained at the start and end of each work-rest cycle using a floor-based photocell system (OptoGait) and a high-speed video camera at 120 Hz. Repeated-measure analysis of variance (trial × time) showed that with time, step width decreased (p = .024) while percent crossover steps increased (p = .008) from the 40th min onwards. Reduced stance time variability (−11.1%, p = .029) step width variability (−8.2%, p = .001), and percent crossover step (−18.5%, p = .010) were observed in ICE compared with CON. No differences in step length and most temporal variables were found. In conclusion, changes in frontal plane gait characteristics may indicate exertional heat stress during prolonged load carriage, and some of these changes may be mitigated with ice slurry ingestion.